1. Field of the Invention
The present invention relates to an AlGaInN-based semiconductor LED device, and a method for manufacturing the same. In particular, the present invention relates to means for basically solving problems caused by application of reverse voltage involved with conventional AlGaInN-based semiconductor LED element having a single p-n junction.
2. Description of the Related Art
Conventional p-n junction LED elements may be broken due to momentary reverse voltage or static electricity externally applied thereto or involve potential defects caused by non-specific static electricity because its breakdown voltage (Vr) against reverse voltage is low, for example, several ten volts. For this reason, such conventional p-n junction LED elements exhibit degraded reliability.
In order to solve this problem, the present invention is adapted to integrate an LED element with a reverse p-n junction protective element, so as to prevent reverse voltage applied to the LED element from flowing through the LED element while operating the protective element to absorb the reverse voltage, thereby protecting the LED element from damage caused by the reverse voltage.
Referring to FIG. 1, a conventional AlGaInN-based LED element is illustrated. As shown in FIG. 1, the LED element includes a sapphire substrate 10 as an insulating substrate. The LED element also includes, a buffer layer 11, an n type GaN layer 12, an InGaN (or GaN) active layer 13, a p type GaN layer 14, a transparent electrode 15, a protective film 16, an n type metal electrode 17, and a p type metal electrode 18, which are laminated on the sapphire substrate 10.
This structure is a p-n junction diode structure in which holes introduced into an active layer through a p-electrode are coupled, in the active layer, with electrons introduced into the active layer through an n-electrode, thereby emitting light corresponding to a band gap of the composition of the active layer material in accordance with the principle of a general compound semiconductor optical element. In accordance with electrical characteristics of a general p-n junction LED element, current flows through the LED element at the level of a threshold voltage Vth when a forward voltage is applied to the LED element. On the other hand, when a reverse voltage is applied to the LED element, no or little current flows through the LED element until the applied voltage reaches the level of a breakdown voltage −Vr. When the applied voltage exceeds the breakdown voltage −Vr, current flows sharply (FIG. 2). Such a breakdown voltage −Vr is determined by the doping concentration and crystallinity of the p-n junction. In the case of an AlGaInN-based LED, its breakdown voltage is typically several ten volts (10 to 50V). When the p-n junction in such an LED has an increased doping concentration to maintain the operating voltage of the LED to be low, the breakdown voltage of the LED may be decreased to, for example, a range of 10 to 20V). In this case, however, the LED may be susceptible to external static electricity, so that it may be broken. Otherwise, the p-n junction of the LED may be damaged, so that the reliability of the LED may be gradually degraded. In particular, since static electricity is frequently generated during a process of assembling the element, reverse voltage applied to the LED has great influence on the reliability and yield of the element. For this reason, application of reverse voltage is an important problem to be handled.